Origin of Jurassic coal seam gas, SE Queensland

Authors / CoAuthors

Boreham, C.J. | Draper, J. | Hope, J.M.

Abstract

With coal seam gas becoming an increasingly important contributor to the energy sector in eastern Australia, a critical factor is to understand the source of this gas, enabling migration fairways to be inferred and to access the risk of gas alteration and loss from source to reservoir. The paper will detail the use of stable carbon and hydrogen isotopic composition of individual coal seam gas components (methane, C2+ hydrocarbons and CO2) in determining the origin of the coal seam gases. The gas samples are from recent appraisal drilling by Queensland Gas Company Limited and Arrow Energy N.L. in the Jurassic Walloon Coal Measures, eastern Surat Basin, and are supplemented by Permian coal seam gas of a wide geographic distribution from the eastern (Moura and Peat ? Oil Company of Australia) and western margins of the underlying Bowen Basin (Fairway ? Tipperary Oil and Gas (Australia) Pty Ltd). The isotopic analyses from the coal seam gases are also compared with natural gases from conventional sandstone reservoirs in the Surat and Bowen basins. For methane from the Jurassic coals the carbon isotopes show a very narrow range from ?13C -57.3 to -54.2 ?. This compares to the much wider isotopic range for methane from the Permian coals (?13C -79.9 to -22.9 ?), reflecting a `continuum? from biogenic (isotopically light) to thermogenic (isotopically heavy) sources. On the other hand, the natural gases are isotopically heavy (?13C -43 to -31.9 ?), consistent with their thermogenic source from Permian coals and associated disseminated organic matter. Similarly, the hydrogen isotopes show a restricted range from ?D -215.5 to -203.3 ? compared with methane from Permian coals of ?D -255 to -152 ?. On the other hand, the carbon isotopes of the associated C2+ hydrocarbons (?13C -43.9 to -24.5 ?) are similar for the Jurassic coal seam gases and the conventional natural gases, suggesting a common thermogenic source for the wet gas components. Thus, the isotopic data for the hydrocarbon gases supports a mixed origin from local Jurassic coals and Permian sources. The former is the predominant source given that the associated CO2 is mostly isotopically light, ?13C range from -8 to -32 ?, and primarily sourced from decarboxylation of immature Jurassic coals.

Product Type

nonGeographicDataset

eCat Id

60933

Contact for the resource

Custodian

Point of contact

Commonwealth of Australia (Geoscience Australia)
Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia

Keywords

External PublicationAbstract

( Theme )

hydrocarbons

( Theme )

organic geochemistry

( Theme )

petroleum exploration

AU-QLD

Australian and New Zealand Standard Research Classification (ANZSRC)

Earth Sciences

Published_Internal

Publication Date

2004-01-01T00:00:00

Creation Date

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Australian Government Security ClassificationSystem

Classification - unclassified

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Creative Commons Attribution 4.0 International Licence

Access - restricted

Use - license

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Purpose

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unknown

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geoscientificInformation

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Unknown

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Spatial Resolution

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Associations

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